One reason for no-horn tieflings (Aside from the ones mentioned already):
It allows more hair options to customize tieflings. The hairstyles they have not feels really limited compared to other races (and they are not as nice looking in my opinion). I did use a mod to unlock more hairstyles but the issue there is that so many clip badly with horns and it made me sad (Which likely explains why they have limited hairstyles, to avoid that sort of clipping).
